Monorail board considering single track between stations

By Mike Lindblom
Seattle Times staff reporter

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That would be a significant departure from the traditional monorail concept, in which a pair of tracks run side-by-side. With single tracks, the northbound and southbound trains would take turns using each segment of the line.

Parallel tracks would be built at stations to allow trains going in opposite directions to pass. Sophisticated computer systems would be needed to keep the automated trains from running into each other.

Single-tracking is being considered mainly for aesthetic reasons, said board Chairman Tom Weeks. The columns could be smaller and tracks would cast smaller shadows..

The agency's Green Line committee this morning unanimously endorsed further studies of single-tracking. The concept was praised by two private-industry construction teams competing to build the project.

Besides making the line less visually intrusive, single-tracking is also likely to reduce its construction cost. This is because a much smaller underground foundation would be needed to support a single track. .

Tax revenues to fund the $1.75 billion project are coming in one-third below predictions, and it appears likely the agency will need to trim $200 million or more.

The downside of single-tracking is that the monorail probably could never achieve the performance of double-track systems like Vancouver SkyTrain, where trains routinely arrive every 90 seconds at rush hour and every two to four minutes at other times. Joel Horn, the monorail's executive director, has instructed engineers to aim for an average peak-period passenger wait of 2½ minutes.

The system'speople-moving capacity would also be reduced, although Horn said the Green Line should still be able to meet the goal of 3,000 persons per hour per direction promised in last year's voter-approved monorail plan.

It may not be advisable to single-track along Second Avenue downtown because that is expected to be the area of heaviest use and dual tracks would move more people, officials said. But they haven't ruled out single-tracking there.

Several landowners have objected to what they consider the visual blight of a monorail on Second Avenue, and some have proposed building the project only from Ballard to Westlake Center and from West Seattle to King Street Station, with no tracks through downtown.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com

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